The jobs of building an offshore plant, a large vessel, and/or the like is classified into industries where accidents of workers frequently occur in the middle of working at a building workplace. Therefore, a building workplace of an offshore plant, a large vessel, and/or the like needs a system which monitors locations of workers to effectively handle risk situations of the workers.
However, since a process of building an offshore plant, a large vessel, and/or the like is performed in a closed indoor workplace, it is difficult to monitor locations of workers by using location tracking technology based on a global positioning system (GPS).